Dual-element thin-film magnetic head including a composite lower core

ABSTRACT

An inductive thin-film magnetic head with small flucuations of the reproduction output and noises for reproduction is disclosed. The forward end of each of a lower an upper magnetic and an upper magnetic core has the same width as the track. The rear end of each of the lower magnetic core and the upper magnetic core, on the other hand, is wider than the forward end thereof in the direction of the track. Also, the lower magnetic core is formed of at least two magnetic layers with a non-magnetic layer interposed therebetween.

BACKGROUND OF THE INVENTION

The present invention relates to a novel inductive thin-film magnetichead for a dual-element thin-film magnetic head unit including aninductive thin-film magnetic recording head and a magnetoresistivereading head.

With the recording density of a magnetic disk apparatus ever on theincrease, magnetic coercive force of the magnetic recording medium isincreased while the track width of the inductive thin film magnetic headused for recording is decreasing. Also, the downsizing of the magneticdisk apparatus has reduced the reproduction output of the inductivethin-film magnetic head. For this reason, an inductive thin-filmmagnetic head is used as a recording head, and a magnetoresistive headis used for converting the leakage magnetic field from the medium as aresistance change. The magnetoresistive head includes a sensorconstituted of a magnetoresistive element, a giant magnetoresistiveelement, a ferromagnetic tunnel junction element, etc., and one of themagnetic shields for improving the spatial resolution is shared with oneof the magnetic cores of the inductive thin-film magnetic head.

The current trend of the shape of the magnetic core along theair-bearing surface of an inductive thin-film magnetic head is such thatthe width of the upper magnetic core determines the track width and thewidth of the lower magnetic core serving also as the upper shield filmof the reproductive head is several tens of times larger than the trackwidth. With the decrease in track width, however, the magnetic fieldexpanding out of the track ends has become conspicuous.

In order to solve this problem, the structure of an inductive thin-filmmagnetic head with the upper portion of the lower magnetic core of theinductive thin-film magnetic head is shaped to the same width as theupper magnetic core is described in U.S. Pat. No. 5,438,747. Also, thestructure of the inductive thin-film magnetic head having a trenchincluding a pole tip layer with the width thereof defining the trackwidth is described in JP-A-7-296328 laid open Nov. 10, 1995 andcorresponding to the U.S. patent application Ser. No. 229,484 filed Apr.19, 1994.

The inductive thin-film magnetic head described in U.S. Pat. No.5,438,747 (JP-A-7-262519) and JP-A-7-296328 has a protrusion structurehaving substantially the same width as the track in the neighborhood ofthe air-bearing surface in the upper portion of the lower magnetic core.This protrusion structure facilitates the machining of the track to awidth in the order of submicrons, and the magnetic fields areconcentrated in the protrusion structure.

SUMMARY OF THE INVENTION

The prior art described above may develop a magnetic domain wall in thecorners of the magnetic material. In the case where the lower magneticcore of the inductive thin-film magnetic head doubles as the uppermagnetic shield of the reproductive head, therefore, a domain wall mayoccur in the portion of the upper magnetic shield extending from the endof protrusion structure to the neighborhood of the sensor portion of thereproductive head. This domain wall is moved by the leakage magneticfield from the medium or the change in the external magnetic field,thereby posing the problem of output changes.

Accordingly, the object of the present invention is to provide adual-element thin-film magnetic head with small fluctuations of thereproduction output and small reproduction noises.

According to one aspect of the invention, there is provided an inductivethin-film magnetic head comprising a lower magnetic core formed on asubstrate, an upper magnetic core arranged in opposed relation to thelower magnetic core with a magnetic gap film therebetween, a coilinterposed between the lower magnetic core and the upper magnetic core,and a dielectric layer for insulating the lower magnetic core, the uppermagnetic core and the coil from each other, wherein the forward ends ofthe lower magnetic core and the upper magnetic core have the same widthas the track, and the rear ends of the lower magnetic core and the uppermagnetic core have a width larger than the width of the forward endsthereof.

According to another aspect of the invention, there is provided aninductive thin-film magnetic head, wherein the lower magnetic corepreferably is formed of at least two magnetic layers with a non-magneticlayer therebetween and the forward end of each of the magnetic layers incontact with a magnetic gap has the same width as track.

According to an embodiment of the invention, an inductive thin-filmmagnetic head comprises a lower magnetic core formed on a substrate, anupper magnetic core having its forward end thereof coupled to the lowermagnetic core through a magnetic gap film and its rear end thereofcoupled to the lower magnetic core, the forward end being smaller inwidth than the rear end thereof, the width being made progressivelysmaller from the rear end toward the forward end thereof, a coilarranged to surround the upper magnetic core and the lower magneticcore, and a dielectric layer formed between the coil, the upper magneticcore and the lower magnetic core, wherein a protrusion structure havingthe same width as the track is formed at least on the portion of thelower magnetic core in the neighborhood of the air-bearing surface and anon-magnetic layer is formed at least in the neighborhood of theair-bearing surface between the lower magnetic core and the protrusionstructure.

Preferably, the thickness of the non-magnetic layer between the lowermagnetic core and the protrusion structure is smaller than the thicknessof the magnetic gap film, and the saturation magnetic flux density ofthe protrusion structure is not less than 1.3 T.

According to another embodiment of the invention, the non-magnetic filmis held between the lower magnetic core and the protrusion structureformed on the lower magnetic core of an inductive thin-film magnetichead. In this way, the magnetic coupling between the lower magnetic coreand the protrusion structure is reduced in order that no domain wall isformed in the neighborhood of the sensor of the reproductive head. Theoutput fluctuations and noises of the reproductive head which otherwisemight be caused by the generation, extinction and relocation of thedomain wall can be reduced.

The non-magnetic film between the lower magnetic core and the protrusionstructure of the inductive thin-film magnetic head should besufficiently thin to reduce the magnetic coupling between them to suchan extent as not to form any domain wall in the neighborhood of thesensor of the reproductive head of the lower magnetic core. In the casewhere the non-magnetic film is thicker than the gap film, thenon-magnetic film would function also as a gap, with a result that therecording magnetic field would be made wider with its intensity beingmade correspondingly smaller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the forward end of an inductivethin-film magnetic head according to an embodiment of the presentinvention.

FIGS. 2a, 2 b are diagrams showing the manner in which the lowermagnetic core of the inductive thin-film magnetic head is magnetized.

FIGS. 3a, 3 b are diagrams showing the shape of the air-bearing surfaceof the inductive thin-film magnetic head according to an embodiment ofthe invention.

FIGS. 4a, 4 b are diagrams showing the in-plane component of themagnetic field strength of the inductive thin-film magnetic headaccording to an embodiment of the invention.

FIG. 5 is a perspective view of the forward end of the inductivethin-film magnetic head according to an embodiment of the invention.

FIG. 6 is a schematic diagram showing a hard disk device according to anembodiment of the invention.

FIG. 7 is a sectional view of an inductive magnetic recording headaccording to an embodiment of the invention.

FIG. 8 is a perspective view showing a part of a magnetic headcomprising an inductive magnetic recording head and a magnetoresistivereproductive head integrated with each other according to an embodimentof the invention.

FIG. 9 is a general view of a magnetic disk device according to anembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

FIG. 1 is a perspective view of the portion of the inductive thin-filmmagnetic head in the neighborhood of the air-bearing surface accordingto an embodiment of the present invention. A non-magnetic film 4, anupper layer 12 of a lower magnetic core and a magnetic gap film 3 areformed in that order on a lower layer 11 of the lower magnetic core.Then, a coil and a dielectric layer to surround the lower magnetic core1 and the upper magnetic core 2 are formed. After that, the uppermagnetic core 2 is formed. Last of all, the forward end of the upperlayer 12 of the lower magnetic core is formed to the desired shape byion milling or the like using an appropriate mask and the upper magneticcore 2. A magnetic core of similar shape can be obtained also by formingthe forward ends of the upper magnetic core 2 and the upper layer 12 ofthe lower magnetic core simultaneously by the focused ion beam process.

As shown in FIG. 1, the forward ends of the lower magnetic core and theupper magnetic core both have the same width as the track, whereas therear ends of the lower magnetic core and the upper magnetic core have alarger width than the forward ends thereof in the direction transverseof the track.

Further, the lower magnetic core has two magnetic layers through anon-magnetic layer therebetween, and the forward end thereof in contactwith the magnetic gap has substantially the same width as the track.

The portion of the lower magnetic core in the neighborhood of theair-bearing surface has a protrusion structure of substantially the samewidth as the track, and at least the portion between the lower magneticcore and the protrusion structure in the neighborhood of the air-bearingsurface has the non-magnetic layer.

FIGS. 2a, 2 b are diagrams showing the magnetic domain structure of thelower magnetic core of the inductive thin-film magnetic head. Thismagnetic domain structure is an example of the result observed using thespin-polarized SEM. Arrows 7 indicate the direction of magnetization.FIG. 2a shows the magnetic domain structure with a non-magnetic film notformed between the upper layer 12 of the lower magnetic core and thelower layer 11 of the lower magnetic core, and FIG. 2b shows themagnetic domain structure with a non-magnetic film formed between theupper layer 12 of the lower magnetic core and the lower layer 11 of thelower magnetic core. In the absence of the non-magnetic film between theupper layer 12 of the lower magnetic core and the lower layer 11 of thelower magnetic core, a domain wall 8 is liable to occur between the stepon a magnetoresistive element 6 and an end of the contact portionbetween the upper layer 12 of the lower magnetic core and the lowerlayer 11 of the lower magnetic core. The magnetization changes so thatthe domain wall 8 occurs, disappears or moves before and after recordingor with the change in the external magnetic field. The domain wall 8,which is at a 180° domain wall in FIG. 2a, may be a 90° domain walldepending on the magnetization. This domain wall 8 and the change in thedirection 7 of magnetization cause the output fluctuations and noises ofthe magnetoresistive element 6. The domain wall is liable to be formedat the tip of the forward end of the upper layer 12 of the lowermagnetic core and the step of a magnetic material by reason of the factthat a magnetic pole is generated in the end portion and the step of themagnetic material.

As shown in FIG. 2b, a non-magnetic film 4 is held between the lowerlayer 11 of the lower magnetic core and the upper layer 12 of the lowermagnetic core thereby to reduce the magnetic coupling between the lowerlayer 11 of the lower magnetic core and the upper layer 12 of the lowermagnetic core. In this way, the lower layer 11 of the lower magneticcore forms a substantially single magnetic domain. In this case, thethickness of the magnetic gap film 3 is set to 0.3 μm and the thicknessof the non-magnetic film 4 is set to 50 nm.

FIGS. 3a, 3 b are diagrams showing the shape of the air-bearing surfaceof the inductive thin-film magnetic head according to an embodiment ofthe invention.

FIG. 3a shows the state in which the upper layer 12 of the lowermagnetic core has not been cut for a sufficiently long time so that theupper layer 12 of the lower magnetic core still remains on thenonmagnetic film 4 other than the track area. In this case, thenon-magnetic film 4 between the upper layer 12 of the lower magneticcore and the lower layer 11 of the lower magnetic core reduces themagnetic coupling between them. Therefore, the possibility is very lowof a domain wall being generated in the portion of the lower layer 11 ofthe lower magnetic core in the neighborhood of the track, but thepossibility is high of a leakage magnetic field increasing from thetrack end in the direction transverse of the track. For the leakagemagnetic field to be reduced in the direction transverse of the track,the cutting depth of the upper layer 12 of the lower magnetic core isrequired to be not less than 0.3 μm.

FIG. 3b shows the case in which the cutting time is sufficiently long sothat even the surface of the lower layer 11 of the lower magnetic coreis cut. In the case where the surface of the lower layer 11 of the lowermagnetic core changes in a curve as gentle as shown in FIG. 3b, noproblem is posed as the domain wall is not easily formed in the portionof the lower layer 11 of the lower magnetic core in the neighborhood ofthe track. Once a step is formed by cutting the lower layer 11 of thelower magnetic core further, however, a domain wall is liable to begenerated from the particular point.

To further suppress the generation of a domain wall, the lower layer 11of the lower magnetic core may be formed of a magnetic multilayer filmhaving an alternate multilayer arrangement of magnetic films andnon-magnetic films.

FIGS. 4a, 4 b show the in-plane component of the magnetic field strengthof an inductive thin-film magnetic head calculated by the integralelement method according to an embodiment of the invention. The magneticcores are configured as shown in FIG. 1. Assuming that the lowermagnetic core 1 is 120 μm wide and made of a permalloy containing 80% Niand 20% Fe, the saturated magnetic flux density Bs is set to 1 T and theinitial permeability μ to 2500. Also, the thickness of the lower layer11 of the lower magnetic core is set to 2.4 μm and the thickness of theupper layer 12 of the lower magnetic core is set to 0.6 μm. Thethickness of the magnetic gap film 3 is set to 0.3 μm, the track widthto 1.2 μm, and the width of the rear end of the upper magnetic core 2 to100 μm. Also, assuming that the upper magnetic core 2 is 4 μm thick andmade of an alloy containing 46% Ni and 54% Fe, the saturated magneticflux density Bs is set to 1.7 T and the initial permeability μ to 1700.The magnetomotive force is set to 0.5 AT, and the magnetic fieldstrength is measured at a point 70 nm away from the air-bearing surfaceof the inductive thin-film magnetic head.

FIG. 4a is a diagram showing the change of the magnetic field toward thetrack on the center line of the inductive thin-film magnetic head.Circles indicate the case in which the non-magnetic film is not formedbetween the lower layer 11 of the lower magnetic core and the upperlayer 12 of the lower magnetic core, and triangles indicate the case inwhich the thickness of the non-magnetic film 4 is 0.3 μm. The negativeside along the abscissa corresponds to the lower magnetic core 1, and inthe case where the thickness of the non-magnetic film 4 is 0.3 μm, theposition indicated by x=−0.9 μm corresponds to the center of thenon-magnetic film 4. In the presence of the non-magnetic film 4, thecentral magnetic field is decreased while the magnetic field in theneighborhood of the non-magnetic film 4 is increased.

FIG. 4b is a diagram showing the magnetic field at the center of the gapand the magnetic field at the center of the non-magnetic film assummarized with respect to the thickness of the non-magnetic film 4. Themagnetic field at the center of the gap decreases with the increase inthe thickness of the non-magnetic film, and the magnetic field at thecenter of the non-magnetic film 4, which increases with the thicknessthe non-magnetic film 4 until the latter reaches 0.3 μm, decreasessubsequently. This indicates that the magnetic field at the center ofthe non-magnetic film increases with the thickness of the non-magneticfilm until the latter reaches the thickness of the magnetic gap film 3,after which the magnetic field decreases. Desirably, the magnetic fieldat the center of the gap is high and the magnetic field at the center ofthe non-magnetic film is low. In other words, the thickness of thenon-magnetic film 4 is desirably not more than the thickness of themagnetic gap film 3, and the thickness of the non-magnetic film 4 isdesirably not more than one third of the thickness of the magnetic gapfilm 3.

Embodiment 2

FIG. 5 shows an inductive thin-film magnetic head according to anotherembodiment of the invention. FIG. 5 is a perspective view of the portionof the inductive thin-film magnetic head in the neighborhood of theair-bearing surface thereof. The non-magnetic film 4 is formed on thelower magnetic core 1, after which the lower layer 91 of the pole tipelement, the magnetic gap film 3 and the upper layer 92 of the pole tipelement are formed in that order. Then, a coil to surround the lowermagnetic core 1 and the upper magnetic core 2 and a dielectric layer areformed, followed by forming the upper magnetic core 2. In the absence ofthe non-magnetic film 4, a domain wall is liable to occur in the lowermagnetic core 1 from the end of the pole tip element 9. The provision ofthe non-magnetic film 4 between the lower magnetic core 1 and the poletip element 9 as in this invention makes it difficult for a domain wallto form in the lower magnetic core 1. According to this embodiment, thepole tip element 9 includes the lower layer 91, the magnetic gap film 3and the upper layer 92. A similar effect can be produced also in theabsence of the upper layer 92 of the pole tip element.

Embodiment 3

FIG. 6 is a schematic diagram showing a hard disk device using aninductive thin-film magnetic head and a magnetoresistive reproductivehead of the spin valve head according to the first and secondembodiments. This device includes a disk rotative shaft 64 and a spindlemotor 65 for rotating the shaft 64 at a high speed. The disk rotativeshaft 64 has mounted thereon one or a plurality (two in this embodiment)of disks 40 arranged at predetermined intervals. Thus each disk 40rotates integrally with the disk rotative shaft 64. The disk 40 is acircular plate having a predetermined radius and a predeterminedthickness and formed with a permanent magnet film on both sides thereofconstituting information recording surfaces. This device also includes ahead positioning rotative shaft 62 and a voice coil motor 63 for drivingthe rotative shaft 62 on the exterior thereof, and a plurality of accessarms 61 are mounted on the head positioning rotative shaft 62. Arecording/reproductive head (hereinafter referred to simply as the head)60 is mounted at the forward end of each access arm 61. As a result,each head 60 is moved in radial direction on each disk 40 with therotation of the head positioning rotative shaft 62 by a predeterminedangle, and set in position. Also, each head 60 is held at a pointseveral tens of nm from the surface of the disk 40 under the balancebetween the buoyancy caused by the high-speed rotation of the disk 40and the pressure of the gimbal constituting an elastic member of theaccess arm 61. The spindle motor 65 and the voice coil motor 63 areconnected to a hard disk controller 66, respectively, whereby therotative speed of the disk 40 and the position of the head 60 arecontrolled.

FIG. 7 is a sectional view schematically showing the inductive recordinghead explained in the first and second embodiments and used with thehard disk device according to an embodiment of the invention. Thisthin-film head includes an upper shield film 186, a lower magnetic core184 made of a magnetic film attached thereon, a dielectric film 4 forisolating the upper shield film 186 and the lower magnetic core 184 fromeach other, and an upper magnetic core 185. A non-magnetic dielectricmember 189 is attached between these magnetic films. A part of thedielectric member defines the magnetic gap 188. The support member is inthe shape of slider having an air-bearing surface (ABS) and is adaptedto be airborne in proximity to the disk medium rotating during the diskfile operation. The forward ends of the lower magnetic core 184 and theupper magnetic core 185 are similar in detail to those in FIGS. 1 and 5.

The thin-film magnetic head has a back contact 190 formed by the uppermagnetic film 185 and the lower magnetic film 184.

According to an embodiment of the invention, each coil 187 made of asingle layer is in the shape of a slightly deformed ellipse, of whichthe portion having a smaller sectional area is arranged nearest to themagnetic gap with the sectional area progressively increasing with thedistance from the magnetic gap.

A multiplicity of the elliptical coils are inserted with a comparativelyhigh density between the back gap 190 and the magnetic gap 188. In thisarea, the width and the section diameter of the coils are small.Further, the elliptical (flat oval) coils have no sharp corner or edgeor end and are small in current resistance. Also, an elliptical coil, ascompared with a rectangular or circular (annular) coil, can have a shorttotal length of the conductor. These advantages lead to a comparativelysmall resistance, small heat generation and an appropriate degree ofheat radiation of the coils as a whole. Since a considerable amount ofheat is reduced, the deformation, elongation and expansion of thethin-film layer are prevented thereby to eliminate the causes of thepole tip protrusion in the ABS.

The elliptical coil having a substantially uniform width can be attachedby the conventional plating technique inexpensive as compared with thesputtering or vapor deposition. A coil having other shapes, orespecially those having a sharp corner are liable to lack a uniformwidth when attached by plating. By eliminating corners and sharp edges,it is possible to prevent the coil products from being subjected to alarge mechanical stress.

According to this embodiment, a multiplicity of turns of substantiallyelliptical coils are formed between the magnetic cores, and the diameterof the coil section progressively increases from the magnetic gap towardthe back gap, thereby reducing the heat generation.

FIG. 8 is a perspective view schematically showing a magnetic headhaving an inductive recording head and a magnetoresistive reproductivehead according to an embodiment of the invention. A substrate 150doubling as a head slider is formed with a reproductive head including alower shield 182, a magnetoresistive film 110, a magnetic domain controlfilm 141 and an electrode terminal 140, a lower layer 186 of the lowermagnetic film, a non-magnetic film 4, an upper layer 184 of the lowermagnetic film and an upper magnetic film 183. The lower gap and theupper gap are not shown. The coils 142 generates a magnetomotive forcein the lower core doubling as the upper shield and the upper magneticcore by the electromagnetic induction, thereby constituting an inductiverecording head.

FIG. 9 is a perspective view showing the whole of a magnetic disk deviceaccording to an embodiment of the invention. This magnetic disk devicecomprises a magnetic disk for recording information, a DC motor (notshown) providing means for rotating the magnetic disk, a magnetic headfor writing and reading information, a positioning unit providing meansfor supporting and changing the position of the magnetic head relativeto the magnetic disk, i.e. an actuator and a voice coil motor. FIG. 9shows the case in which five magnetic disks are mounted on the samerotative shaft thereby to increase the total storage capacity.

It will thus be understood from the foregoing description that accordingto the above-mentioned embodiments of the invention, a dual-element(thin-film magnetic) head with a reading magnetoresistive (thin-filmmagnetic) element with small fluctuations in output signal and reducednoises is obtained.

What is claimed is:
 1. An inductive thin-film magnetic head comprising:a lower magnetic core formed on a substrate; an upper magnetic coreformed in opposed relation to said lower magnetic core with a magneticgap film therebetween; a coil interposed between said lower magneticcore and said upper magnetic core; and a dielectric layer for insulatingsaid lower magnetic core, said upper magnetic core and said coil fromeach other; wherein said lower magnetic core has at least two magneticlayers with a non-magnetic layer interposed therebetween.
 2. Aninductive thin-film magnetic head according to claim 1, wherein theforward end of said lower magnetic core in contact with said magneticgap has the same width as the track.
 3. An inductive thin-film magnetichead comprising: a lower magnetic core formed on a substrate; an uppermagnetic core having the forward end thereof coupled to said lowermagnetic core through a magnetic gap film and the rear end thereofcoupled to said lower magnetic core, said upper magnetic core having awidth progressively decreasing from the rear end toward the forward endthereof; a coil arranged to surround said upper magnetic core and saidlower magnetic core; a dielectric layer formed between said coil, saidupper magnetic core and said lower magnetic core; and wherein said lowermagnetic core has a first magnetic layer having a protrusion structure,a second magnetic layer with a width that is larger than that of saidprotrusion structure and a non-magnetic layer formed between said firstmagnetic layer and said second magnetic layer; and said protrusionstructure faces to said magnetic gap film.
 4. An inductive thin-filmmagnetic head according to claim 3, wherein the thickness of saidnon-magnetic layer between said lower magnetic core and said protrusionstructure is smaller than the thickness of said magnetic gap film.